Switch



March 23, 1937. J. SCHMIDINGER 2,074,345

I SWITCH Original Filed Feb. 9, 1934 2 Sheets-Sheet l INVENT OR ATTORNEY March 23, 1937. J SCHMlDlNGER 2,074,345

SWITCH 7 Original Filed Feb. 9, 1934 2 Sheets-Sheet 2 IN VEN IOR A TTORNE Y6 Patented Mar. 23, 1937 I I 2,074,345

UNITED STATES PATENT OFFICE SWITCH Joseph Schmidinger, Long Island City, N. Y.

Application February 9, 1934, Serial No. (L408 Renewed June 11, 1936 22 Claims. (Cl. 200-113) This invention relates to electric switches and which is adapted to be connected to one pole of more specifically to thermo-responsive electric a source of potential. The other end of the strip switches. is maintained in a position such that the strip An object of the invention is to provide a deis constrained to assume a buckled configuration.

vice of the character described, which is efli- This may be accomplished by attaching an excient, economical and readily manufactured. tension l3 to the screw it, which is associated Other objects are to provide a device adapted with the base l0 and which is adapted to be conto be inserted in an electric system to alter perinected to the other pole of the source of potenodically the effective current through the system tial. The extension l3 and the screw l4 may by breaking the main circuit or by changing the form with the strip H, a continuous electrically- 10 elements comprising the system; and to provide conducting path. Means may be provided for such a device wherein an element, which changes varying the configuration or amount of buckling position so as to change electric circuits, is of the strip; for example, one or more wings l5 adapted to move slightly at first and thereafter may connect the extension l3 to the upright l6 to move farther and/or more rapidly; and to of an L-Shaped member ll, attached to the base. 15 provide such a device with an element having This attachment may be by means of the screw such a property due to that elements characterl4. Suitable means for varying the position of istic of flexing in a predetermined part after suffithe upright 16, which upright may be resilient, cient displacement or deformation of another may be provided such as the screw it associated part of the element has set up certain stresses with the upright l9, which extends from the base of suflicient intensity in said predetermined part. H). An axial motion of the screw will overcome 20 Other objects of the invention will in part be the resilience of the upright l6 and move the obvious and will in part appear hereinafter. latter so as to change the position of the exten- The invention accordingly comprises the feasion l3 of the strip ll, thereby changing the tures of construction, combinations of elements, constraint and the configuration of the latter.

and arrangement of parts, which will be exem- An electrically-conducting thermally-responplifled in the construction hereinafter set forth sive element 20 attached to an intermediate porand the scope of the application of which will tion of the strip ll connects the latter to a secbe indicated in the claims. 0nd pole of the source of potential. This ther- For a fuller understanding of the nature and many-responsive element is preferably a wire of 30 objects of the invention reference should be had such character and size as to be almost instanto the following detailed description taken in taneously responsive to changes in current transconnection with the accompanying drawings, in mitted therethrough by alterations in its length.

which: The electrical connection between the strip ll 5 Fig. 1 is a plan view of a device embodying one and the second pole of the source of potential form of the invention; may be accomplished by attaching the wire to a Fig. 2 is a side view in elevation, partly in secresilient conducting member ll, which is in contion, of the device shown in Fig. 1; tact with the screw i2. The thermally-respon- Fig. 3 is a view similar to Fig. 2 of a modificasive wire 20 is preferably so aifixed to the strip ll tion of the device shown in Figs. 1 and 2; as to alter the normal position of the strip by 40 Fig. 4 is a diagrammatic view of one element overcoming the tendency of the strip to buckle in of the device shown in Figs. 1-3, in different apredetermined way, and causing it to buckle in positions; a different manner, as hereinafter explained.

Fig. 5 is a diagram of the electric circuits in Such an action of the thermally-responsive the device shown in Figs. 1 and 2; resistance wire may be effected by mounting the 5 Fig. 6 is a diagram of the electric circuits in wire between the strip and the supporting memthe device shown in Fig. 3; her ll under tension, so that when the wire is Fig. 7 is a view, similar to Fig. 2, of a modificacooled and contracted it acts to effect the desired tion of the device shown in Figs. 1 and 2; and distortion of the buckled strip H. The tension Fig. 8 is a view, similar to Fig. 2, of a modifiof the wire 20 may be controlled in a manner 50 cation of the device shown in Figs. 1 and 2. like that previously described in connection with In the drawings, the numeral lfl denotes a base the control of the strip H, by means of a screw above which is supported in any convenient l8 mounted rigidly in the upright l9 extending fashion, a conducting strip ll. One end of the from the base I0 and bearing against the memstrip may be insulatedly attached to a screw l2, ber ll. 55

By adjustment of the screw a slight change in the position of the member I? may be secured with a corresponding change in the tension of the thermally-responsive wire 20. It has been found 5 that the action of the wire 20 on the strip II may be most efiectlvely transmitted if the wire is connected to the strip through a pin or similar element 2| rigidly mounted on the strip I I. With such a structure a pivoting action of a kind is secured by expansion and contraction of the wire 20, which is highly effective in obtaining the desired alteration in the shape of the strip I I.

The electrically conducting member 22, which preferably may be resilient, and which, in the embodiment of the invention shown in Figs. 1, 2 and 5, is connected to the second pole of the source of potential, is provided at its free end with a contact 23 adapted to mate with a contact 24 on strip II when the strip is in its normal position. When the contacts 23 and 24 are mated,

the wire 20 is shunted.

In the embodiment of the invention shown, for example, in Figs. 1, 2 and 5, any operative unit, such as the lamp 25, may receive sufiicient our- 25 rent to function only when the contacts are together, where the resistance of the member 22 is relatively small and the resistance of the thermally responsive wire 20 is relatively large. It will be understood that such a unit, however,

if it requires only a small amount of current, may be positioned in series with the wire 28, (see Fig. 7) so as to be shunted with it when the contacts 23 and 24 mate, in which case the operative unit 25 will be energized only when the contacts are apart, 1. e., when the wire 20 and the unit are not shunted.

The operation of the device shown in Figs. 1, 2 and 5 is as follows: The buckled conducting element I I is so mounted that its normal position is that shown, for example, by the dotted lines in Fig. 4. The element is preferably so designed that its portion of greatest strength is approximately at the end of the element to which the wire 20 is affixed, and more particularly that portion of the element lying immediately adjacent the pivoting post 2|. The element is preferably weakened at or about the place where the contact 24 is carried, so that this portion of the element exerts relatively little opposition to changes in position caused by an. alteration of the position of that portion of the element lying adjacent the pin 2|. In its normal position the element 20 is preferably so buckled that the contact carrying portion is sprung upwardly against the resilient element 22, so that the contacts 23 and 24 are mated.

As has already been pointed out, the wire 20 is preferably so mounted as to distort the element H from its normal position, the wire 20,

when cold, exerting such a tension on that portion of the strip to which it is attached through the pivot pin 2| as to distort the strip II at that point, so that the contact-carrying portion of the strip is bowed downwardly, as shown for example by the full lines in Fig. 4, in which position the contacts 23 and 24 are in disengaged position. This is the normal condition of the device when no current is being passed through it.

When potential-is applied to the device, ourrent passes through the circuit comprising the post 12, the supporting member H, the resistance wire 20, the pivoting post 2I, the short end of the element I I and its extension I3, and the pole l4. The passage of the current through this circuit causes the wire 20 to heat and expand. As

it expands the element II tends to assume its normal position, i. e., the contact 24 gradually approaches the contact 23 because of the inherent spring tension in the element I I. When the contact 24 has reached a critical point where that portion of the element II carrying it buckles upwardly, as shown by the dotted lines in Fig. 4, instead of downwardly, as shown by the full line therein, the contact 24 is thrown violently against the contact 23 and against the resiliency of the member 22.

When the device is in this condition the circuit comprises the post I2, the element 22, the mated contacts 23, 24, the element II and its extension l3, and the post I4. The wire 20 is shunted and tends immediately to cool and contract. As it contracts it forces the post 2I to pivot downwardly against the spring tension of the relatively heavy portion of the element II. This in turn causes the contact 24 to be pulled away from the contact 23, which remains mated with it and which follows it for a short distance because of the resiliency of the member 22. When, however, the contraction of the wire 20 has reached a point where the element II is buckled in such a manner as to assume its original position, the contacts are caused to separate rapidly by the toggle-like action of that portion of the element II carrying the contact 24.

It will be understood that the periodic alteration in the circuits within the device and the periodic mating and breaking of the contacts causes a periodic fluctuation in the intensity of the current transmitted through the device so.

that lamps in circuit therewith, for example, are caused to flash and become periodically brilliant and dim.

The adjustable elements described permit an adjustment of the tension of either or both the elements I I and 20, whereby the period of utilization of each circuit within the device may be controlled independently or with respect to the other circuit in such a manner that the rapidity of fluctuation of the period of utilization of each circuit may be controlled.

The resiliency of the member 22 is preferably such that its elastic limit is in no wise approached by the motion set up in it during the change in position of the strip II. The resilient member 22 exerts an important function in tending to keep the contacts together for a definite period during the preliminary contraction of the wire 20, whereby the shunting circuit may be maintained for such a time as to prevent a mere sputtering or excessively rapid fluctuation in the device. Where a shunting circuit such as is disclosed in Figs, 1, 2 and 5 is employed, sparking between the contacts is prevented.

In the embodiment of the invention shown in Figs. 3 and 6, no shunting circuit is provided. The resilient member 22 is electrically connected to one pole of the source of potential, as for example the screw I I, and the thermally responsive resistance wire 20 is electrically connected to the other pole of the source of potential, as for example to the screw I2. The buckled strip I I is insulated from both poles. The member 22 is so positioned with respect to the strip II that the contacts 23 and 24 engage only when the wire 20 is cooled and contracted, and thus distorts the element II so as to force the contact-carrying portion thereof down against the contact carried by the resilient member 22.

The operation of a device comprising this embodiment of the invention, and shown for exthe resilient element 22, and the post I4 is enerelement I I.

gized. The wire 20 becomes heated and expands. Its tension against the spring action of the strip II diminishes. The strip tends to assume its normal position and the contact 24 commences to move away from the contact 23. The contacts, however, remain in mated condition due to the resiliency of the arm 22 until a critical point in the alteration of the shape of the element II is reached, i. e., until the element tends to assume the shape shown, for example, by the dotted lines in Fig. 4.

At this point the contact 24 is snapped away from the contact 23 by toggle-like action of the The circuit is broken. The wire 20 commences to contract immediately and to exert a distorting effect upon the element II, causing the contact 24 to be forced gradually downwardly into mating position with the contact 23. When the contraction of the wire 20 has reached a stage where the critical point in the position of the element II is reached, the toggle-like action of the element snaps the contact 24 into violent engagement with the contact 23 against the action of T the resilient arm 22. It will be apparent that even though the circuit is completely broken by a device such as is shown, for example, in Fig. 3, the rapid snapping action effected by the element II in controlling position of the. contact 24 results in so rapid a separation and mating of the contacts as to reduce sparking to a minimum. There, is no tendency whatever for the contacts to pull gradually apart or to approach a mating position slowly. The contacts are snapped apart and snapped into mating position by the action of the element II.

The duration of the completed circuit with respect to the duration of the broken circuit in the operation of the device may be controlled by adjusting the relative tensions of the resistance wire 20 and the element II in the manner described in connection with the device shown in Figs. 1, 2 and 5.

Although the thermally responsive resistance wire has been shown in every case as connected to the spring element II through a pivot post, it is to be understood that any other direct connection between the wire and the element, or any indirect connection which does not destroy the functions of the elements, may be employed without departing from the scope of the invention. Where the thermally responsive wire is directly connected to the element Il without the interposition of a pivot post it may be desirable to so position the wire that the force it exerts against- Save for the thermally responsive resistance wire itself, and the slight movement of the resilient contact-carrying arm, the device has been simplified to a point where only a single movable element is employed. This element, the buckled spring element I I, has been so designed and positioned in the structure as to effect a completely novel contact making and breaking action. This single movable element has been so designed that it operates first to cause an exceedingly slow approach or withdrawal of the movable contact to or from the fixed contact. This feature of the design of the buckled element, in cooperation with the resiliency of the fixed contact-carrying'arm, permits the device to function in such a way that each circuit within the device is in operation for an appreciable time, so that even slow, regular periodic flashes may be obtained in lamps placed in circuit with the device.

The buckled element II also acts to separate rapidly the contacts or rapidly to cause them to mate after the first slow approaching .or withdrawing action has reached a predetermined point. This feature prevents sputtering or sparking of the contacts, insures their long life, and where an oxide tends to form on the contacts, for example, where tungsten contacts are employed, the snapping action incidental to a mating of the contacts is with such force that the contacts are hammered together so vigorously as to shake free from their surfaces the accumulated oxide. Furthermore, there is a slight wiping or sliding action of the contacts, one on the other, during the period in which they are in contact, with the result that tendency to pit and to oxidize on the surfaces of the contacts is still further reduced.

In the structural form shown in the preferred embodiments of the invention, the entire device may be encased in a small, compact closure, with only the adjusting screws available.

The term oppositely bowed as used in the claims is intended to include such action wherein the curvature or the bow of. the strip I I is changed from one position to another so that the circuit through the strip is closed when the strip is in one position and broken when the strip is in the other position.

Since certain changes may be made in the above construction and different embodiments of theinvention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for normally being in one predetermined position of equilibrium and when stressed for moving into the other equilibrium position, thermo-responsive means directly secured to said constrained means and adapted under certain conditions for stressing said constrained means, and means adapted for altering the temperature of said thermo-responsive means whereby said constrained means constantly moves from one position of equilibrium to another.

2. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for carrying a contact and for normally being in one predetermined position of equilibrium and when stressed for moving into the other equilibrium position, a second contact engaging said first contact in one of said positions, and thermo-responsive means directly secured to said constrained means and adapted under certain conditions for stressing said constrained means.

3. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for carrying a contact and for normally being in one predetermined position of equilibrium and when stressed for moving into the other equilibrium position, a second contact engaging said first contact in one of said positions, thermo-responsive means directly secured to said constrained means and adapted under certain conditions for stressing said constrained means, and means for causing said second contact to tend to resist the motion of said carried contact in one direction and to follow the motion of said. carried contact-in another direction.

4. In a device of the character described, the combination comprising constrained means adapted for being in equilibrium in oppositely bowed configurations and for being in unstable equilibrium in at least one intermediate configuration and for carrying a contact, a second contact engaging with said first contact when said means are in one equilibrium configuration, and thermo-responsive means directly secured to said constrained means and adapted for changing the configuration of said constrained means from one equilibrium to another.

5. In a device of the character described, the combination comprising constrained means adapted for being in equilibrium in oppositely bowed positions and for being in unstable equilibrium in at least one intermediate position and for carrying a contact, a second contact engaging with said first contact when said means are in one equilibrium position, and thermo-responsive means directly secured to said constrained means and adapted for changing the position of said constrained means from one equilibrium to another.

6. In a device of the character described, the combnation comprising constrained means adapted for being in equilibrium in oppositely bowed positions and for 'being in unstable equilibrium in at least one intermediate position and for carrying a contact, a second contact engaging with said first contact when said means are in one equilibrium position, current-carrying thermo-responsive means directly secured to said constrained means and adapted for changing the position of said constrained means from one equilibrium to another, and means adapted for altering the potential across said thermo-responsive means when said contacts engage.

7. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for normally being in one predetermined position of equilibrium and when stressed for moving into the other equilibrium position, thermo-responsive means directly secured to said constrained means and adapted under certain conditions for stressing said constrained means, and means adapted for altering the temperature of said thermo-responsive means while it is stressing said constrained means so iat it ceases to stress said constrained means and while it is not stressing said constrained means so that it begins to stress said constrained means.

- 8. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for normally being in one predetermined position of equilibrium and when stressed for moving into the other equilibrium position, thermo-responsive means directly secured to said constrained means and adapted under certain conditions for stressing said constrained means, and means adapted for altering the temperature of said thermo-responsive means while it is stressing said constrained means so that it ceases to stress said constrained means and while it is not stressing said constrained means so that it begins to stress said constrained means, said altering means comprising an electric circuit passing at least in part through said thermo-responsive means.

9. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for normally being in one predetermined position of equilibrium and when stressed for moving into the other equilibrium position, thermo-responsive means directly'secured to said constrained means and adapted under certain conditions for stressing said con strained means, and means adapted for altering the temperature of said thermo-responsive means while it is stressing said constrained means so that it ceases to stress said constrained means and while it is not stressing said constrained means so that it begins to stress said constrained means, said altering means comprising an electric circuit passing at least in part through said thermo-responsive means and controlled by the position of said constrained means.

10. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for normally being in one predetermined position of equilibrium and when stressed for moving into the other equilibrium position, thermo-responsive means directly secured to said constrained means and adapted under certain conditions for stressing said constrained means, means adapted for altering the temperature of said thermo-responsive means while it is stressing said constrained means so that it ceases to stress said constrained means and while it is not stressing said constrained means so that it begins to stress said constrained means, said altering means comprising an electric circuit passing at least in part through said thermo-responsive means and controlled by the position of said constrained means, and means .for varying .the constraint on said constrained means.

11. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for normally being in one predeterm ned position of equilibrium and when stressed for moving into the other equilibrium position, thermo-responsive means directly secured to said constrained means and adapted un- Cil der certain conditions for stressing said constrained means, means adapted for altering the temperature of said thermo-responsive means while it is stressing said constrained means so that it ceases to stress said constrained means and while it is not stressing said constrained means so that it begins to stress said constrained means, said altering means comprising an electric circuit passing at least in part through said thermo-responsive means, a contact carried by said constrained means, a second contact adapted to engage said first contact when said constrained means is in one of said positions, and means adapted for shunting that part of said circuit in said thermo-responsive means when said contacts engage.

12. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for normally being in one predetermined position of equilibrium and when stressed for moving into the other equilibrium position, thermo-responsive means directly secured to said constrained means and adapted under certain conditions for stressing said constrained means, means adapted for altering the temperature of said thermo-responsive means while it is stressing said constrained means so that it ceases to stress said constrained means and while it is not stressing said constrained means so that it begins to stress said constrained means, said altering means comprising an electric circuit passing at least in part through said thermo-responsive means, a contact carried by said constrained means, a second contact adapted to engage said first contact when said constrained means is in one of said positions, and means adapted for breaking said circuit when said contacts engage.

13. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for normally-being in one predetermined position of equilibrium and when stressed for moving into the other equilibrium position, thermo-responsive means directly secured to said constrained means and adapted under certain conditions for stressing said constrained means, means adapted for altering the temperature of said thermo-responsive means while it is stressingsaid constrained means so that it ceases to stress said constrained means and while it is not stressing said constrained means so that it begins to stress said constrained means, said altering means comprising an electric circuit passing at least in part through said thermoresponsive means, a contact carried by said constrained means, a second contact adapted to engage said first contact when said constrained means is in one of said positions, means adapted for shunting that part of said circuit in said thermo-responsive means when said contacts engage, and means for causing said second contact to tend to resist the motion of said carried contact in one direction and to follow the motion of said carried contact in another direction.

14. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for normally being in one predetermined position of equilibrium and when stressed for moving into the other equilibrium position, thermo-responsive means directly secured to said constrained means and adapted under certain conditions for stressing said constrained means, means adapted for altering thev temperature of said thermo-responsive means while it is stressing said constrained means so that it ceases to stress said constrained means and while it is not stressing said constrained means so that it begins to stress said constrained means, said altering means comprising an electric circuit passing at least in part through said thermo-responsive means, a contact carried by said constrained means, a second contact adapted to engage said first contact when said constrained means is in one of said positions, means adapted for breaking said circuit when said contacts engage, and means for causing said second contact to tend to resist the motion of said carried contact in one direction and to follow the motion of said carried contact in another direction.

15. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for normally being in one predetermined position of equilibrium and when stressed for moving into the other equilibrium position, thermo-responsive means directly secured to said constrained means and adapted under certain conditions for stressing said constrained means, means adapted for altering the temperature of said thermo-responsive means while it is stressing said constrained means so that it ceases to stress said constrained means and while it is not stressing said constrained means so that it begins to stress said constrained means, said altering means comprising an electric circuit passing at least in part through said thermo-responsive means, a contact carried by said constrained means, a second contact adapted to engage said first contact when said constrained means is in one of said positions, and means adapted for shunting that part of said circuit in said thermo-responsive means when said contacts engage, said constrained means comprising a longitudinally-constrained, doubly-flexed, strip of flexible material and said thermo-responsive means comprising a wire connected to said strip.

'16. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for normally being in one predetermined position of equilibrium and when stressed for moving into the other equilibrium position, thermo-responsive means directly secured to said constrained means and adapted under certain conditions for stressing said constrained means, means adapted for altering the temperature of said thermo-responsive means while it is stressing said constrained means so that it ceases to stress said constrained means and while it is not stressing said constrained means so that it begins to stress said constrained means, said altering means comprising an electric circuit passing at least in part through said thermo-responsive means, a contact carried by said constrained means, a second contact adapted to engage said first contact when said constrained means is in one of said positions, and means adapted for shunting that part of said circuit in said thermo-responsive means when said contacts engage, said constrained means comprising a longitudinally-constrained, doubly-flexed, strip of flexible material, said thermo-responsive means comprising a wire connected to said strip, and said circuit comprising at least a portion of said strip in parallel with said wire.

17. In a device of the character described, the combination comprising constrained means arranged to assume oppositely bowed positions of equilibrium and adapted for normally being in one predetermined position of equilibrium and when stressed for moving into the other equilibrium position, thermo-responsive means directly secured to said constrained means and adapted under certain conditions for stressing said constrained means, means adapted for altering the temperature of said thermo-responsive means while it is stressing said constrained means so that it ceases to stress said constrained means and while it is not stressing said constrained means so that it begins to stress said constrained means, said altering means comprising an electric circuit passing at least in part through said thermo-responsive means, a contact carried by said constrained means, a second contact adapted to engage said first contact when said constrained means is in one of said positions, and means adapted for shunting that part of said circuit in said thermo-responsive means when said contacts engage, said constrained means comprising a longitudinally-constrained, doubly-flexed, strip of flexible material, and said thermo-responsive means comprising a wire connected to said one of the fiexures in said strip and in such a manner as to change under varying conditions the curvature of said fiexure.

18. In a device of the character described, in combination, a pair of contacts, means adapted for giving said contacts a difference in potential and comprising a thermo-responsive resistance wire, means comprising a doubly-flexed member arranged to assume oppositely bowed positions of equilibrium, the flexure of which is controlled by said wire, for giving said contacts a diiferent difference in potential, said wire being directly secured to said doubly-flexed member, and means comprising a plurality of electric circuits adapted to cause a periodic alteration in the length of said wire.

19. In a device of the character described, the combination comprising a constrained member of spring material operative to different positions of equilibrium and rigidly fixed at both ends and constrained to cause it to tend toassume one of said positions, said constrained member having a portion intermediate the ends of weaker construction than the portion adjacent one end, the latter portion being adapted to be flexed in opposition to the inherent constraint of the member to cause the same to assume a second position of equilibrium, thermo-responsive means connected with the said second named portion of the said constrained member and adapted under certain conditions to flex the same and cause it to assume the last named position of equilibrium, and means for altering the temperature of the said thermo-responsive means.

20. In a device of the character described, the combination comprising a constrained member of spring material operative to difierent positions of equilibrium and rigidly fixed at both ends and constrained to cause it to tend to assume one of the said positions, the said constrained member having a portion intermediate its ends of weaker construction than the portion adjacent one end, the latter portion being adapted to be flexed in opposition to the inherent constraint of the member to cause the same to assume a second position of equilibrium, a rigid flexing element fastened to the said last named portion, thermo-responsive means connected with the said element and adapted under certain conditions to flex the constrained member and to cause it to assume the last named position of equilibrium, and means for altering the temperature of the said thermo-responsive means.

21. In a device of the character described, the combination comprising a member of spring material constrained between two points of support and being a part operative to different control positions of equilibrium, the said member having a portion adjacent to one end biased to cause the said part to tend to assume one of said positions of equilibrium but adapted to be flexed in opposition to the inherent bias thereof to cause the said part to assume a second position of equilibrium, thermo-responsive means connected with said biased portion and adapted under certain conditions to flex the same and to cause the said part to assume the last named position of equilibrium, and means for altering the temperature of the said thermo-responsive means, the said member of spring material being of progressively diminishing strength from the said biased portion to the said part.

22. A device of the character set forth in claim 21, in which the constrained member is a metallic strip which is reduced in width at points intermediate its ends to form the said portion of weaker construction.

JOSEPH SCHMIDINGER. 

